It is a fact that the primary method of oil production results in the production of only about 5 to 20 percent of the oil present within the formation. Various secondary recovery methods are known. The adoption of secondary recovery techniques has been somewhat inhibited by their low efficiency, high operating costs, and other problems relating to environmental condemnation, geological disturbances and the like. One known method of secondary recovery involves the steaming of oil well formations from the surface. This procedure is commonly referred to as "huffing and puffing". The existing method of secondary recovery using steam is characterized by many serious problems and disadvantages which have particularly plagued the oil industry in the last four or five years during which various developments in the world have focused attention on secondary recovery.
The problems with the existing steaming procedures include the fact that the steam is generated in very large boilers which must operate at temperatures of 500.degree. F. to 900.degree. F. in order to produce the steam at 250.degree. F. to 450.degree. F. required at the pay zone. These large boilers are positioned on the surface and require elaborate site preparation and very expensive equipment to withstand the thermal stresses generated by the temperatures involved. In addition, vast lengths of steam lines are required for distribution of the super-heated steam from the boiler to the various wellheads within the field. The steam lines result in major heat losses which substantially reduce the overall thermal efficiency of the operation. The steam lines, even though provided with numerous expansion loops, are subject to cracking and breaking as a result of thermal stress and vibration.
Another major facet of the problems is that existing steaming procedures are adapted to an absolute maximum well depth on the order of 2500 to 3000 feet and the full length of the well is normally steamed during steam injection. Most of the wells being steamed today are only from about 700 to 1500 feet in depth. Thus, the existing steaming technique is not adapted to the secondary recovery of oil from deeper pay zones. However, there exists in the United States many areas in which the pay zone is deeper than 3000 feet and from which oil is potentially producible.
It has also been previously proposed to inject water into the bore hole and then to heat the water. This procedure is of limited efficacy because the water is not as effective in penetrating many pay zones. Further, the down hole heating of water entails the heating of water admixed with the naturally occurring fluids including brines and the like which quickly foul or corrode the heating equipment. The water procedure is also depth limited, as previously mentioned.
The present invention represents a major contribution to the art of secondary oil recovery by mitigating or overcoming the many problems associated with the existing steaming techniques. More particularly, by the practice of the present invention it is possible to dispense with elaborate surface site preparation since no large central boiler system is involved in the practice of this invention. The present invention is adapted to be put into operation in most wells without any major advance preparation other than removal of residual fluid, if any, within the bore hole. Further, the practice of this invention makes possible the injection of thermal energy directly into the pay zone at a preselected depth and at the proper temperature usually ranging from 250.degree. F. to 450.degree. F. No distribution system involving steam lines from a central boiler to the wellhead is utilized. Rather, cold water is pumped down the string of tubing into the tool where it is converted into steam and the steam thus generated is forced out into the formation.
Still further, the practice of the present invention is not limited to any well depth and this invention is fully operable at great depths of 12000 feet or more where secondary recovery by steaming has heretofore been impossible. Thus, in short, the present invention is adaptable to a greater range of well depths, provides greater thermal efficiency through the elimination of heat losses, and obviates the need for elaborate, costly and potentially hazardous surface steam distribution systems.
It is to be anticipated that this invention and the modifications thereof which will occur to those skilled in the art will be rapidly adopted in the petroleum industry.